1. Field of the Invention
This invention relates to a motor vehicle accessory, and more particularly a rear view mirror, angularly adjustable by an electrically driven motor.
2. Prior Art
Rear view mirrors mounted outside a motor vehicle and adjustable from inside the vehicle are known and the advantages are well recognized. The desirability of controlling the adjustment through an electric motor and transmission located within the mirror housing are also recognized and various structures have been proposed in the art for motor operated mirrors. See, for example, U.S. Pat. No. 3,609,014.
As shown by the above mentioned patent, it has been proposed to adjust a centrally pivoted mirror about horizontal and vertical axes using screws connected with the back of the pivoted mirror, and advanced or retracted by rotatable nuts, driven either by separate motors and worms or by a single motor and worm pivoted at the opposite end of the motor to selectively engage one or the other nuts.
As a further example of known systems for electrically adjusting mirrors, the assignee of this application has previously considered an electrically operable mirror similar to that described above using a single electric motor centrally pivoted to engage a worm driven by the motor with one of two rotary nuts to adjust lead screws connected to a pivoted mirror.
The known structures as exemplified above have the disadvantage of requiring relatively expensive mirror supporting plate structure and connections for pivoting and adjusting the mirror relative to a fixed support. The use of a separate electric motor for each screw is, of course, expensive and bulky. A single electric motor pivoted at one end is subjected to inertia forces of the vehicle, which affect the engagement of the drive members. Even where the motor is centrally pivoted, the entire mass of the motor must be swung or pivoted to change engagement of the drive between one rotary nut and the other, and the motor mount of necessity is not firm.
Typically, operation of such motor driven mirrors has been noisy. Analysis has shown the noise is generated from drive motor vibration and over engagement between the worm drive and the worm wheel teeth of the rotary nuts. Additional noise is generated and a certain degree of binding between the nuts and the adjusting screws is created in prior art arrangements, because the typical universal ball type connection between the adjusting screws and the mirror backing, does not fully adjust to maintain accurate axial alignment between the screws and nuts. This can become troublesome at the extremes of the adjustment range.
Also, previous constructions, having a central pivot for the mirror backplate, have typically utilized a number of parts in forming a firm but pivotal connection to a fixed support, including ball and clamping sockets and spring tensioning devices, which require undesirable assembly time in manufacture and which do not always function satisfactorily.
One problem in the use of motor adjusted mirrors has been that the mirrors are sometimes subjected to external forces, for example, through attempts to adjust the mirror angle by hand. In the absence of some accommodation for such forces, the drive mechanism is likely to become damaged in use. Further, in the event the mirror element should be restrained against movement when the adjusting motor is operated, as by snow or ice, between the housing and mirror, the motor in the typical drive arrangement will be stalled and possibly damaged.
A further problem with adjustable external mirrors is that the mirror tends to vibrate relative to the housing, because of the single center pivot support and the use of only two points of support at the adjustment screws, which are generally located quite centrally of the mirror where the housing has the most depth to accommodate the adjusting mechanism and where the extent of axial movement of the adjusting screws is minimized for a given angular adjustment. A "nervous image" results from this vibration, and viewing through the mirror is difficult.